1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming system, and an image forming method.
2. Description of the Related Art
An electro photographic image forming apparatus forms a latent image on a photoreceptor based on image data and develops the latent image as a toner image. The developed toner image is transferred on a sheet through a transfer unit. The image forming apparatus of such a type as to temporarily transfer the toner image on an intermediate transfer unit, transfers the toner image on the intermediate transfer unit on a sheet through a transfer unit corresponding to a secondary transfer unit.
To reliably perform transfer, these transfer units perform transfer by attracting the negatively charged toner image by positively charging a back side of the sheet, to a front side of the sheet. Thereafter, a fixing device fixes the toner image on the sheet and ejects the sheet on which the toner image is fixed to a paper ejection tray.
Some of these image forming apparatuses have two modes of a sheet ejection mode in which a sheet on which a toner image is fixed is ejected without being reversed, and a sheet ejection mode in which a sheet is reversed and ejected (see, for example, Japanese Patent Laid-Open No. 2007-168116). These image forming apparatuses are configured to be able to switch over between the above-described sheet ejection modes for each job to facilitate job-basis segmentation.
In the above-described image forming apparatuses, because positive charge is given to the back side of the sheet during transfer of the toner image on the sheet as described above, the surface on which the toner image is formed is negatively charged after the transfer of the toner image, and the opposite surface to which positive charge is given is positively charged.
When the sheet charged as described above is ejected to the paper ejection tray, if the sheet is ejected in the same manner of faces as the previously ejected sheet, the positively charged face of the ejected sheet overlaps with the negatively charged face of the previously ejected sheet, which possibly causes problems that the sheets stick to each other or it is difficult to align the sheets. These problems become prominent when post-processing is performed on the sheets. These problems prominently occur, in particular, in prints in the field of PP (Production Printer).
The image forming apparatus of Japanese Patent Laid-Open No. 2007-168116 switches over between two modes of the sheet ejection mode in which the sheet is ejected without being reversed and the sheet ejection mode in which the sheet is reversed and ejected for each job. However, with this image forming apparatus, it is impossible to prevent sheets ejected in the same job from sticking to each other.
Further, in view of the above-described problems, there is a proposed image forming apparatus that eliminates charge of a sheet after image transfer using a charge eliminating blower (see Japanese Patent Laid-Open No. 10-181969). Further, there is a proposed image forming apparatus provided with a first charge eliminator and a second charge eliminator cause to reliably eliminate charges (see Japanese Patent Laid-Open No. 2004-10240). However, with these image forming apparatuses, it is difficult to ensure eliminating charge and it is still impossible to ensure preventing sheets from sticking to each other.
The present invention has been made in view of the above circumstances and has at least one object to provide an image forming apparatus, image forming system and image forming method, which prevent the sheets, which are charged, from sticking to each other.